由于某种原因，在尝试对ODE系统进行数值求解时，它会变为全零。我认为这意味着不稳定的解决方案，但总的来说，我认为情况将返回无穷大或nan，而不是零。为什么会发生这种情况，我该如何解决？我在运行odeint时收到以下警告（尽管它仍在完成）：

Warning

python\python37\lib\site-packages\scipy\integrate\odepack.py:236: ODEintWarning: Excess work done on this call (perhaps wrong Dfun type). Run with full_output = 1 to get quantitative information. 


 warnings.warn(warning_msg,ODEintWarning)

代码

import scipy as sp
from scipy.integrate import odeint
import numpy as np

def ODEEq(rho,t,D,B,Nd):
    return (D*np.gradient(np.gradient(rho))-B*(Nd*rho+(rho**2)))
def Solver(delz,delt,L,T,G0,Nd,Sf,Sb,unitMaker=1e-9):
    xm1Ghost = G0[1] - (Sf*delz*G0[0]/D)
    xLp1Ghost = G0[-2] - (Sb*delz*G0[-1]/D)
    rho = G0
    np.insert(rho,xm1Ghost)
    np.append(rho,xLp1Ghost)

    sol = odeint(ODEEq,rho,tspace,args=(D,Nd),full_output=1)
    return sol

L = 4000
timeRange = 2000
D = 1.639e18
B = 2e13
Nd = 0
delz = L/(10*L)
delt = timeRange/(10*timeRange)
G0 = 640*np.exp((-6.4e-2)*np.linspace(0,1000,L))
Sf = 0.64
Sb = 0.64

sol = Solver(delz,timeRange,Sb)

结果（sol）：

(array([[6.40000000e+02,6.29838965e+02,6.19839253e+02,...,1.05982469e-25,1.04299825e-25,1.02643897e-25],[3.64489112e+01,3.64037414e+01,3.63580081e+01,1.64712980e-25,1.61424855e-25,1.58213241e-25],[0.00000000e+00,0.00000000e+00,0.00000000e+00],0.00000000e+00]]),{'hu': array([2.24035532e-005,8.91443222e-312,4.78098028e+004,3.21768899e-021,3.11632803e-021,3.01816006e-021]),'tcur': array([1.28018934e-003,2.65545333e-021,4.31714361e-049,4.15062501e-049,3.98753839e-049]),'tolsf': array([ 0.00000000e+000,-4.85590765e+004,5.32418663e-009,5.23965656e-009,5.15646853e-009]),'tsw': array([2.54756216e-004,4.83671586e-009,5.52645557e-023,5.40880326e-023,5.29122707e-023]),'nst': array([        500,420,2051404512,-901543794,-382763050,-1396204354],dtype=int32),'nfe': array([     52989,896695326,-858716839,-564525364],'nje': array([        13,604126608,1834441325,1211124015,1163472949],'nqu': array([         5,414912656,-441395200,1046325818,744409088],'imxer': -1,'lenrw': 16036022,'leniw': 4020,'mused': array([         2,67999744,1022034837,973886464],'message': 'Excess work done on this call (perhaps wrong Dfun type).'})